In the detergent industry, distinctions are drawn between cleaning compositions on the basis of their functional utility. For example, there are considerable art-recognized differences between cleaning compositions that are used for laundering purposes; cleaning compositions that are used for machine dishwashing purposes; and cleaning compositions that are used for hand dishwashing purposes. Generally, cleaning compositions for laundering purposes employ high foaming organic surfactants as the main cleansing agents. Foaming, unless it is excessive to the extent that it causes overflow from the washing machines, is generally considered beneficial in laundering compositions because it provides an indication to users that the product is working. By way of contrast, machine dishwashing methods which are currently used to wash china, glass, porcelain, ceramic, metal, and hard synthetic articles impart a high mechanical impact of the wash liquid which is sprayed onto the articles to be cleaned. Recently, developments in dishwashing apparatus have been directed toward further increasing the intensity of liquid motion as well as the water volume cycled per minute, so as to further improve the mechanical cleansing effect of the cleansing solution. Compared to laundering compositions, however, machine dishwashing compositions are very low-foaming compositions inasmuch as foam formation interferes with the mechanical action of the dishwasher and reduces the mechanical impact of the liquid sprayed onto the articles to be cleaned. The surface active agents useful for machine dishwashing compositions should not only be low foaming materials, but they should also be foam depressants, so that the foaming caused by protein and food residues in combination with alkaline cleansing solutions is kept to a minimum. This situation, however, is quite different from hand dishwashing compositions, which, preferably, are high foaming and have more the attributes of laundering compositions.
Thus, machine dishwashing detergents constitute a generally recognized class of detergent compositions. In summary, machine dishwashing detergents are mixtures of ingredients whose purpose, in combination, is to emulsify and remove food soils; to inhibit the foam caused by certain food soils; to promote the wetting of dinnerware to thereby minimize or eliminate visually observable spotting; to remove stains such as those caused by coffee and tea; to prevent a buildup of soil films on dinnerware surfaces; and to reduce or eliminate tarnishing of flatware. Additionally, machine dishwashing detergents must possess these characteristics without substantially etching or corroding or otherwise damaging the surface of dinnerware and flatware.
It is conventional to use strongly alkaline solutions in institutional and household dishwashing machines for washing dishes, glasses, and other cooking and eating utensils. Ordinary tap water is used to make up the strongly alkaline cleaning solution and for rinsing purposes subsequent to the cleaning operation. However, spotting on dishes and glassware by hard water and soil residues and precipitates has been a major problem. Currently these problems are minimized in machine dishwashing detergent compositions by the use of relatively high levels of polyphosphates to act as hardness sequestering agents, thus reducing the amount of hardwater deposits and filming on glassware. In addition, these detergents usually contain a chlorine bleaching system for stain removal and an added cleaning boost by oxidizing protienacious soils on glassware. Chlorinating agents also help prevent spotting.
Although the performance of these conventional detergent compositions are quite satisfactory, high phosphate levels have potential environmental drawbacks. Furthermore, the addition of chlorine bleach requires special processing and storage and packaging precautions. Additionally, chlorine bleach imparts an undesirable odor and makes fragrancing the finished product more difficult.
In recent years, increased attention has been focused upon environmental pollution problems (e.g. water pollution). Phosphates have been identified as a contributing factor to eutrophication (i.e. promotion of algae growth) and considerable effort has been devoted to attempts at replacing all or at least some significant part of the alkaline condensed phosphates used in machine dishwashing detergents with chemicals that are more ecologically acceptable. Of the numerous compounds that have been tested as substitutes for alkaline condensed phosphates (particularly as substitutes for sodium tripolyphosphate), very few chemicals have given promising results. Many chemicals lack the desired cleaning ability. Other chemicals lack the building effect of the polyphosphates which promote cleaning even when used at levels lower than that required to sequester all the hard water metal ions present. Still others are as much or more ecologically undesirable and are too expensive to be practical.
It is not conventional to replace the condensed polyphosphates in dishwashing detergents with carbonate salts. Although carbonate salts are effective and economical water softeners, they remove water hardness ions by precipitation and as a result leave unacceptable levels of residue on the dishes, glassware and utensils being washed.
It is desirable, therefore, to provide a moderately alkaline, low-phosphate, non-chlorine automatic dishwashing detergent composition which provides excellent glassware spotting and filming results. It is especially desirable to provide a detergent composition which imparts glassware cleaning efficacy equal to that of conventional automatic dishwashing detergents which rely on high levels of phosphates and chlorine bleach to achieve the same results. It would also be desirable to provide a stable, less alkaline detergent composition which requires no expensive barrier packaging for extended shelf-life stability.